Currently available temperature-responsive fast battery chargers are designed to stop a fast-charge cycle when the battery reaches a predetermined temperature which is representative of the battery having attained full charge. In one design, a thermostat is contained within a package along with the battery. In a second design, the thermostat is contained within a charger base adjacent the location of the battery being charged.
In any event, when the supply of charging current continues after the battery has attained full charge, the temperature of the battery rises to a level whereby the thermostat opens and terminates the fast-charge operation. Users of this type of charger generally encounter no problems provided that the battery is sufficiently cooled when placed initially in the charger for the charging operation.
However, at times, a battery which is contained in a package with the thermostat may be at or above the trip temperature prior to insertion into the battery charger. In this condition, the thermostat will be open and will not allow the fast-charge cycle to begin until the battery cools sufficiently. Obviously, this delays the charging time and necessitates continued attendance by the user until the battery has cooled sufficiently to permit the charging cycle to begin assuming that the user is aware that the battery is hot.
If a heated battery is placed in a charger where the thermostat is contained within the charger base, the thermostat will require a finite period (perhaps one to two minutes) to respond to the heat of the battery before opening. During this finite period, a charge indicator is providing indication to the user that the fast-charge cycle has begun. Typically, the user proceeds with other tasks unaware that the charger will shut down within a minute or two when the thermostat opens in response to the hot battery. If the thermostat is a manual-reset type, the user will return to find a cooled but uncharged battery.
Thus, there is a need for a thermally-responsive battery charger which will automatically delay the initiation of a charging cycle in the battery is hot when inserted into the charger and will initiate the charging cycle when the battery cools to an appropriate temperature. Further, there is a need for a battery charger which will prevent the charger from reinitiating the charging cycle after the fully charged battery has cooled.